Direct determination of cosmic string loop density from simulations
José J. Blanco-Pillado, Ken D. Olum
Abstract
We determine the distribution of cosmic string loops directly from simulations, rather than determining the loop production function and inferring the loop distribution from that. For a wide range of loop lengths, the results agree well with a power law exponent $\ensuremath{-}2.5$ in the radiation era and $\ensuremath{-}2$ in the matter era, the universal result for any loop production function that does not diverge at small scales. Our results extend those of Ringeval et al. [Cosmological evolution of cosmic string loops, J. Cosmol. Astropart. Phys. 02 (2007) 023.]: we are able to run for 15 times longer in conformal time and simulate a volume 300--2400 times larger. At the times they reached, our simulation is in general agreement with the more negative exponents they found, $\ensuremath{-}2.6$ and $\ensuremath{-}2.4$. However, our simulations show that this was a transient regime; at later times, the exponents decline to the values above. This provides further evidence against models with a rapid divergence of the loop density at small scales, such as ``model 3'' used to analyze LIGO data and predict LISA sensitivity.